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Platypus, Ornithorhynchus anatinus

Fungal Disease: Although the platypus is currently common and widespread, there is concern about the potential impact of an infection caused by an aquatic fungus, Mucor amphiborum. Affected animals develop ulcers on various parts of the body that can lead to death from secondary infection and inability to control body temperature. Further details of the disease are availble on the Department of Primary Industries, Parks, Water and Environment web site.

The platypus, with its duck bill and webbed feet, is a unique Australian animal. It and echidnas are the only monotremes or egg-laying mammals to be found on earth. The marsupials (mammals with pouches, e.g. kangaroos) and eutherians (placental mammals that give birth to well developed young, e.g. humans) both give birth to live young. The monotremes have lower body temperatures than other mammals and have legs which extend out, then vertically below them, resulting in a gait that resembles a reptilian waddle rather than a straight-line gait. These features, together with their egg-laying, are more like that of a lizard than a mammal.

Description

Click upon the movie to view (2.1Mb)

Platypus are readily identified by their streamlined body, webbed feet, broad tail and characteristic muzzle or bill which is rubbery and contains no true teeth. Since platypus dive repeatedly for food, they generally are only sighted when they briefly return to the surface to breathe. Then the top of their head, back and tail can be seen – like the tip of an iceberg, the rest remains submerged.

An adult platypus is from 45 cm to 60 cm in length, with females generally smaller than males. Average platypus size increases with latitude, with the platypuses in north Queensland generally being the smallest where males average about 1 kg. Tasmanian platypus are relatively huge, with some adult males weighing up to 3 kg.

Its usual colouration is deep brown on the back and sides of the head, body and upper surfaces of the limbs. The underside is a golden or silky grey. They have two layers of fur -- a dense waterproof outercoat and a grey woolly underfur to provide much needed insulation. The fur on the broad flat tail is coarse and bristly. They have a smooth swimming action together with a low body profile and no visible ears, making them easily recognisable in the water. It could only be mistaken for a water rat, but these have a long thin tail with a white tip.

The webbed fore-paw is used for swimming, and on land, the skin, which extends beyond the long claws, is folded back to enable the animal to walk or burrow. The webbing on the hind foot does not extend beyond the bases of the claws and this foot is used mainly for steering and to tread water. The tail acts as a powerful rudder when swimming and also aids the animal when diving.

The male has a spur on the inner side of each hind limb, which is connected by means of a hollow groove to a poison gland. This spur is used to inflict wounds on natural enemies and other males, and may possibly play some part in mating. The poison is capable of inflicting a very painful injury to humans.

Surprisingly, platypus are capable of many vocalisations including a soft growling sound when disturbed.

Take a listen to this rarely heard growl!

See also some video footage taken by a keen amateur fisherman - Randall Roberts of Deloraine - who was going fishing in the Meander River at Deloraine when he saw 'a strange rock starting to move':

Distribution and habitat

The platypus is widespread in the eastern states of Australia, in the streams and rivers predominantly east of the Great Dividing Range. They occupy a wide range of habitats and climates, from tropical rainforest streams in the lowlands of north Queensland to alpine lakes in Tasmania at up to 1000 m above sea level. In Tasmania, platypus are widely spread across the state and are common in the lakes of the Central Highlands as well as the rivers and streams of the south, south-west and north-west coasts.

Platypus are semi-aquatic and require access to freshwater habitats to forage, and earth banks to dig their burrows. Ideal platypus habitat includes rivers or streams with earth banks consolidated by the roots of native vegetation, abundant invertebrate prey, cobbled or gravel substrates, overhanging shady vegetation and a sequence of pools and riffles. However they can also occupy lakes and farm dams and even can be found in some streams moderately degraded by human activities.

Burrowing

Platypus spend around half their day resting in short, oval-shaped burrows of about 3 to 8 m long that they dig into earth banks around rivers, lakes or streams. They often have multiple burrows scattered along their home range and adults typically occupy a burrow alone, although different platypuses may use the same burrow on different days. Females also dig elaborate nesting burrows around 20 m long with multiple chambers and earth plugs which they share with their unweaned young.

Swimming and diving

Platypus use their webbed front feet for swimming. On land, the webbing, which extends beyond the long front claws, is folded back to enable the animal to walk and burrow. Platypus have powerful front legs and rely on them for the hard work of both paddling and digging. The webbing on the hind feet does not extend beyond the bases of the claws; the hind legs are used mainly for steering and to tread water while they chew food at the surface.

The tail acts as a rudder when swimming and also aids the animal when diving. It is also where the platypus stores much of its body fat. Biologists use the thickness of the tail to measure an individual’s body condition.

Although platypus are strong swimmers, they are not fast and prefer slow-flowing streams.

Senses

Platypus have small eyes but acute sight. They only open their eyes above water and are particularly good at detecting movement on the river bank. Their hearing is also acute, with a range of hearing similar to the frequencies that humans can detect, but with sensitivity to lower frequency sounds that we can't hear. Little is known about their sense of smell and taste. However males secrete a musky odour from a scent gland in the breeding season so it seems likely that they would have a reasonable sense of smell.

Underwater, platypus rely on touch and a special sixth sense called electro-reception. Monotremes are the only mammals to have developed electro-reception. Sharks and rays use electro-reception to detect prey and can pick up the tiny electrical fields produced by the muscular contraction of their prey. Underwater footage shows platypus swinging their heads from side to side (see video clip above), to detect tiny changes in the electrical field generated by their prey and determine its location.

Behaviour and Diet

Platypus are solitary animals that only come together to mate, although several individuals may be found living in the same section of habitat. Generally they leave their burrows around dusk, forage all night and return around dawn but some animals can also be active in the early morning or evening.

Platypus forage for food for about 12 hours every day and can consume 13-28% of their own body weight in food a day. They dive for between 20-40 seconds during foraging, generally in shallow water less than about five metres deep, and often rest on the surface chewing for only 10 seconds between dives. They can perform about 75 dives per hour.

During dives, platypus are searching for small invertebrate animals on the bottom, including crustaceans, worms and molluscs, as well as the larvae of many freshwater insects. Once caught, these small prey are carried to the surface in cheek-pouches and then eaten. Platypus have no teeth, but instead have small, horny pads which they use to hold and grind their prey.

In some areas platypus spend a surprising amount of time out of water, crossing land between water bodies - even foraging for worms and other invertebrates in waterlogged paddocks.

Grooming of the fur is important to keep the animal’s pelt in good condition and is carried out in the water or on land.

Breeding

Mating occurs during spring but is generally earlier in the north of Australia than in the south. Mating takes place in the water and, after about 21 days, between one and three eggs are laid in a nesting burrow constructed by the female.

The eggs are incubated between the belly and the tail of the female and hatch after about 10 days. Like the echidna, the platypus lacks nipples. Milk from the mammary glands oozes through the skin along both sides of the mother's belly where it is then sucked up by the young platypuses. By six weeks, the young are furred, have their eyes open and may leave the burrow for short intervals and enter the water. When about four months, old the young are weaned.

Venom glands and spurs

Male platypuses have spurs on the inside of their hind legs which are attached to crural glands that produce a powerful venom. Male platypuses can inflict extremely painful wounds in humans, while the venom is capable of killing other animals such as dogs that attack them.

Platypuses are one of only five known venomous mammals but the precise role of the spur and venom is not fully understood. The spurs can inflict wounds on natural predators or other males, and may possibly play some part in the breeding behaviour of the species. The crural gland increases in size during the breeding season and the volume of poison produced increases.

Conservation status

The platypus is totally protected throughout Australia. Although still common in many parts of its range, it is vulnerable to the continuing degradation of suitable water bodies caused by agriculture, damming, drainage and pollution. The illegal netting and trapping of fish also causes many platypus deaths, as do dogs and vehicles.

There also is also concern about the potential impact of an infection to Tasmanian platypus caused by a fungus, Mucor amphiborum. Affected animals develop ulcers on various parts of the body that can lead to death from secondary infection and an inability to control body temperature. Find out more about platypus fungal disease and be sure to report any sightings of diseased platypus.

How you can help

Do not allow your dog to roam in areas where platypuses might occur. Dogs can pose a considerable threat to platypuses and other native animals. When walking with your dog along rivers, streams or other habitat that might be home to a platypus, please keep your dog on a lead.

Where possible leave trees or other vegetation around creeks, waterholes and dams. If clearing willows, resist the temptation to 'clean up the river', make sure blackwood, tea tree or other plants replace them.

Keep farm or household chemicals such as pesticides away from areas where platypus may be found. Do not use pesticides if there is a chance of rain as they may be washed into creeks before they have soaked in.

Use bridges rather than culverts on new tracks or roads. Platypus will not swim through culverts if the water flow is too uniform or fast. They will cross the road instead and are often hit by traffic while doing so.